Ortstreue in foraging ants of the Formica rufa group - hierarchy of orienting cues and long-term memory

Route fidelity and site allegiance (Ortstreue) ofFormica rufa group ants are analysed with repect to orienting cues and preservation through periods of isolation or winter dormancy. Colour-marked workers showed certain site allegiance to different parts of a moundnest, but the phenomenon was too weak to explain the retention of extranidal Ortstreue measurad in nature. The same applies to kinesthetic and other cues based on intranest architecture. Evidence is presented that extranidal Ortstreue is based on long-lasting individual memory of spatially organized visual cues. The engram stored through several months of winter dormancy can be indirectly identified with a representation of landmark/canopy patterns. The experiments carried out in large openair arenas show, however, that olfactory cues, probably identical with scent markings of the home range, are a cause of idiosyncratic Ortstreue during the dark period. The latter orienting cues, which in the main are switched off in the presence of visual cues, may also be stored in the memory, but preservation through winter dormancy could not be confirmed. The possibility that the ants may use geomagnetic cues was tested, but the result was negative. The ecological implications of the findings are discussed.